I encounter this Error: Multiple different uvs per loop at single vertex. when trying to export the model into mod3
Hello fellow MHW modder!

I hope you have latest add-on build, support for 2.8 isn't ready yet (as of post)
https://www.nexusmods.com/monsterhunterworld/mods/969?tab=files

You want to select your seams and break them from the model. 
For some reason the MT Framework engine (or add-on) doesn't like edge loops.
I'm still struggling with some of the other stuff.

Basically on your mesh, 
(first make sure you have triangulated faces, add-on will break and show an error)
Use the edge select, select your seam, press "V" to break (island) it off the mesh.

Here's more about this if you still need help: 
https://github.com/Ezekial711/MonsterHunterWorldModding/wiki/How-to-Fix-UVs-for-Objects-Sharing-Seams